linux-kernel - Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2]

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Message-ID: <543BBCEA.4080202@redhat.com>
Date:	Mon, 13 Oct 2014 07:52:10 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	Stephen Boyd <sboyd@...eaurora.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lenny Szubowicz <lszubowi@...hat.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem
 to be held for duration of changing governors [v2]



On 10/13/2014 06:43 AM, Viresh Kumar wrote:
> On 1 August 2014 22:48, Stephen Boyd <sboyd@...eaurora.org> wrote:
>> On 08/01/14 03:27, Prarit Bhargava wrote:
>>>
>>> Can you send me the test and the trace of the deadlock?  I'm not creating it with:
>>>
>>
>> This was with conservative as the default, and switching to ondemand
>>
>> # cd /sys/devices/system/cpu/cpu2/cpufreq
>> # ls
>> affected_cpus                  scaling_available_governors
>> conservative                   scaling_cur_freq
>> cpuinfo_cur_freq               scaling_driver
>> cpuinfo_max_freq               scaling_governor
>> cpuinfo_min_freq               scaling_max_freq
>> cpuinfo_transition_latency     scaling_min_freq
>> related_cpus                   scaling_setspeed
>> scaling_available_frequencies  stats
>> # cat conservative/down_threshold
>> 20
>> # echo ondemand > scaling_governor
>>
>>  ======================================================
>>  [ INFO: possible circular locking dependency detected ]
>>  3.16.0-rc3-00039-ge1e38f124d87 #47 Not tainted
>>  -------------------------------------------------------
>>  sh/75 is trying to acquire lock:
>>   (s_active#9){++++..}, at: [<c0358a94>] kernfs_remove_by_name_ns+0x3c/0x84
> 
> Can you please retry this on mainline? I wasn't able to reproduce it
> now over 3.17.
> I am trying this on Exynos b.L implementation..

I have 100% reproducibility on latest mainline.

Viresh, please see my next post on the locking issues in cpufreq.

P.

> 
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